Influence of thermal reactive crosslinking agents on the tack,peel adhesion,and shear strength of acrylic pressure-sensitive adhesives

In recent decades, the basic technology of pressure-sensitive adhesive (PSA) acrylics has developed into a sophisticated science. The main properties of acrylic PSAs such as tack, peel adhesion, and shear strength are determined to a large extent by the kind and quantity of crosslinking agents added to the synthesized PSAs. In order to improve their adhesive (tack, peel adhesion) and cohesive (shear strength) properties, a wide range of amino resin thermal crosslinkers are tested. An acrylic PSA based on 2-ethylhexylacrylate, n-butyl acrylate, and acrylic acid was synthesized by performing a radical polymerization in ethyl acetate. After the addition of amino resins to the acrylic PSA and carrying out thermally initiated crosslinking processes to prepare one-sided self-adhesive tapes, their properties were assessed.     

Syntheses and properties of a series of amphiphilic polyacrylamides bearing two long alkyl chains and phosphatidylcholine analogous groups in the side chains

A novel vinyl monomer 2-{(3-acrylamidopropyl)dimethyl ammonio}ethyl 2′-isopropyl phosphate (AAPI) having phosphatidylcholine analogous moiety and a series of new acrylamide monomers containing two long alkyl chains [stearyloleylacrylamide (SOAAm), distearylacrylamide (SSAAm), and n-docosyloleylacrylamide (DOAAm)] were synthesized and characterized. The polyacrylamides ( Va, Vb , and Vc ) were obtained from radical copolymerization of SOAAm, SSAAm, or DOAAm with AAPI in the presence of AIBN as an initiator. The investigations of these copolymers were carried out by x-ray analysis method, DSC, TG-DTA, and viscosity measurement, respectively. The copolymer Vb containing distearyl groups as hydrophobic side chains shows a crystalline state at room temperature, and the ordered structure disappears at high temperature. The phase transition from a crystalline state to a liquid-crystalline state was observed obviously only for copolymer Vb . In addition, the II-A isotherms and A-T isobars of these copolymers were measured and their stable LB films were also prepared. © 1996 John Wiley & Sons, Inc.     

Synthesis and thermal behavior of side-chain liquid crystalline polymethacrylates containing tolane-based mesogenic side groups

The synthesis and characterization of nine polymethacrylates containing 4-alkoxy-4′-trifluoromethyltolane, 4-alkoxy-4′-cyanotolane, and 4-alkoxy-4′-nitrotolane side groups were described in this study. The phase behavior of the prepared monomers and polymers was characterized by differential scanning calorimetry, optical polarizing microscopy, and x-ray diffraction. All of the obtained monomers exhibit no mesophase, while most of the synthesized polymers reveal enantiotropic mesomorphism. The polymethacrylate containing 4-propanyloxy-4′-nitrotolane side groups was the only one which shows no mesomorphic behavior. Both the spacer length and the nature of terminal groups have profound influence on the phase transition temperatures and thermal stability of the mesophase. The polymers with longer spacers tend to form a more ordered mesophase with a wider temperature range. Among three polymers with the same spacer length, the polymer with a trifluoromethyl terminal end group is inclined to form a more ordered mesophase than the other two polymers. No side chain crystallization occurred for all obtained polymers. © 1994 John Wiley & Sons, Inc.     

Comparison between thermal crosslinkers based on melamine-formaldehyde and benzoguanamine resin and their influence on main performance of acrylic pressure-sensitive adhesives as tack,peel adhesion,shear strength and pot-life

An acrylic pressure-sensitive adhesive (PSA) was synthesized in ethyl acetate at about 80 °C by the use of 2-ethylhexyl acrylate, ethyl acrylate, methyl acrylate and acrylic acid at presence of thermal radical initiator AIBN. The synthesized acrylic PSA was crosslinked at relatively low temperatures at about 110–125 °C using thermal crosslinkers selected from melamine-formaldehyde resins and benzoguanamine resins. The crosslinking process runs between carboxylic groups of acrylic PSA and reactive groups from investigated amine resins. The choice of suitable thermal reactive crosslinkers has significant and relevant influence at presence of organic acid catalysts on main performance of crosslinked PSA such as tack, peel adhesion and shear strength.     

Synthesis and characterization of new biodegradable thermosensitive polyphosphazenes with lactic acid ester and methoxyethoxyethoxy side groups

<正>Two novel biodegradable thermosensitive polyphosphazenes with lactic acid ester and methoxyethoxyethoxy side groups were synthesized via the macromolecular substitution reactions of poly(dichlorophosphazene) with the sodium salt of lactic acid ester and sodium methoxyethoxyethoxide.Their structures were confirmed by ~(31)p NMR,~1H NMR,~(13)C NMR,IR,DSC,and elemental analysis.The lower critical solution temperature(LCST) behavior in water and in vitro degradation property of the polymers was investigated.The results indicated that two polymers showed LCST phase transition over a range of concentrations from 0.13 to 15 wt%and pH-sensitive degradation properties.     

Synthesis and properties of poly(acrylamide)s containing both long chain alkyl groups and phosphatidylcholine analogues in the side chains

A series of new phospholipid analogous acrylamide monomers ( 4a–e ) containing long alkyl chains as hydrophobic groups and containing phosphatidylcholine analogues as hydrophilic group were synthesized in high yields. The homopolymerizations and copolymerization ( 4b with 4e ) were carried out in the presence of a radical initiator. The structures and thermal properties of these polymers were investigated by x-ray diffraction analysis, DSC, and polarizing microscopy measurements. It has been revealed that these homopolymers ( 5b, 5c , and 5d ) which bear saturated long-hydrocarbon chains in the side chains exhibited not only orderly stacked bilayer structures at room temperature but also clear liquid crystalline behavior within a wide temperature range. The viscosity behavior of all polymers was found similar to usual polyelectrolytes in porlar solvent. The polymers obtained were also characterized by ¹H-NMR, IR, and melting point, respectively. © 1996 John Wiley & Sons, Inc.     

Designed synthesis and chiroptical properties of regioregular poly(p-phenyleneethynylene-alter-m-phenyleneethynylene) bearing (−)-trans-myrtanoxyl side groups

Two regioregular poly(p-phenyleneethynylene-alter-m-phenyleneethynylene)s bearing (−)-trans-myrtanoxyl side groups with different substitution patterns were designed and synthesized, e.g. Myr-PMPE-1 and Myr-PMPE-2. In Myr-PMPE-1, the side chiral groups are distributed uniformly along the backbone. In Myr-PMPE-2, the distribution of the side chiral groups is alternatively crowded and loose. Both of these two polymers show no CD signal in solutions because of their good solubility. The investigations of chiroptical properties of these two polymers were carried out in the form of spin-coated films. The films were annealed above the glass temperature of the corresponding polymer, and the effects of annealing temperature and time on the properties of the films were investigated by UV-Vis absorption, fluorescence and circular dichroism spectra. The results show that annealing treatment had no significant effect on the properties of Myr-PMPE-1, including UV-Vis absorption, fluorescence and optical activity. The maximum absolute value of dissymmetry factor (|g _max|) was 1.62 × 10⁻⁴. On the other hand, annealing treatment significantly affected the properties of Myr-PMPE-2. Without annealing or being annealed below 100°C, Myr-PMPE-2 films show almost no Cotton effect. In contrast, when annealed above 120°C, the absorption and emission of Myr-PMPE-2 films slightly red shifted with increasing annealing temperature and annealing time. Most importantly, the intensity of CD signals increased significantly and the optical activity of Myr-PMPE-2 films markedly increased. After annealing at 140°C for 4 h, the |g _max| of Myr-PMPE-2 films was increased up to 3.07 × 10⁻³, about one order of magnitude higher than that of Myr-PMPE-1 films. __________ Translated from Acta Polymeric Sinica, 2008, 3 (in Chinese)     

Block copolymers of styrene and n‐alkyl methacrylates with long alkyl groups. Micellization behavior in selective solvents

The micellization properties of well‐defined block copolymers of styrene and decyl methacrylate (SDMA) were studied in two different solvents, methyl acetate (MAc) selective for the polystyrene (PS) block and dodecane, selective for the poly(decyl methacrylate) (PDMA) block. The results were compared with those obtained, in the same solvents, from block copolymers of styrene and stearyl methacrylate (SSMA). In MAc, SDMA copolymers with a decyl methacrylate (DMA) content of 15% or less formed unimolecular micelles, whereas those with a content of 18.5% or higher formed multimolecular micelles. The degrees of association were lower than the corresponding SSMA samples. In dodecane, SDMA form large, monodisperse, spherical, and thermally stable micelles with degrees of association higher than the corresponding SSMA samples. The different behaviors can be attributed to the steric hindrance effect and the ability of the long alkyl groups of the polymethacrylate, MA blocks to crystallize. When the MA blocks are in the soluble corona of the micelles, the steric hindrance effect prevails, thus leading to higher degrees of association for the less bulky alkyl group. In the case where the MA block is in the insoluble core of the micelles, the higher the tendency for crystallization the higher the degree of association. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4177–4188, 2004     

Dynamic mechanical and thermal behavior of liquid-crystalline polybutadiene-diols with mesogenic groups in side chains

Liquid-crystalline polybutadiene-diols (LCPBDs) with the comb-like architecture were synthesized by reaction of a LC thiol with the double bonds of telechelic HO-terminated polybutadiene (PBD). LCPBDs with various initial molar ratios of thiol to double bonds of PBD, R₀, in the range from 0.15 to 1, were prepared by the radical reaction at temperature 60 °C for 48 h. The experimentally obtained degree of modification, R_e, after the reaction and purification, was determined from elemental analysis - from the amount of sulphur bounded in LCPBDs, GPC and from ¹H NMR spectra. The physical properties were investigated by differential scanning calorimetry and dynamic mechanical spectroscopy. With increasing R_e ratio the glass transition temperature of LCPBDs, T_g, increases from ∼ − 45 °C (neat PBD) to ∼20 °C (R_e ∼ 0.5). LC transition starts at R_e ∼ 0.27 (the transition temperature T_m ∼ 27 °C). With increasing R_e temperature T_m increases and for R_e ∼ 0.5 reaches the value T_m ∼ 74 °C; at the same time also the change in enthalpy at LC transition increases. The LC transition could be detected also by the dynamic mechanical spectroscopy; especially shape and position of mechanical functions on frequency and free volume parameters strongly depend on degree of modification.     

Morphology of side chain liquid crystalline block copolymer thin films and effects of thermal annealing

The self-assembly behavior of siloxane based side chain liquid crystalline block copolymer thin films are investigated via grazing incidence small angle X-ray scattering and atomic force microscopy. The as-spun films displayed polystyrene cylinders perpendicular to the substrate and the cylinders reoriented parallel to the surface after thermal annealing. The morphology observed in the as-spun films is resultant from the orientation of the smectic LC mesophase relative to the substrate. Annealing above both the polystyrene glass transition temperature and the smectic to isotropic transition temperature eliminates the influence of the LC phase, leading to a reorientation of the morphology that minimizes the interfacial energy of the system. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3263–3266, 2007     

Synthesis and liquid crystalline behavior of side chain liquid crystalline polymers containing triphenylene discotic mesogens with different length flexible spacers

A series of side chain liquid crystalline polymers(SCLCPs) containing triphenylene(Tp) units in the side chains, denoted as PMTS(without spacer) and PMTn S(n = 2, 3, 4, 6, which is the number of the methylene units between the main chain and Tp moieties in the side chains), with different lengths of spacers were synthesized through conventional free radical polymerization. The chemical structures of the monomers were confirmed by 1H/13C-NMR, and the phase behaviors were examined by differential scanning calorimetry(DSC), polarized optical microscopy(POM) and wide-angle X-ray diffraction(1D and 2D WAXD). The molecular characterization of the polymers was performed with 1H-NMR, gel permeation chromatography(GPC) and thermogravimetric analysis(TGA). The phase behaviors of the polymers have been investigated by a combination of techniques including DSC, POM, 1D and 2D WAXD. The results showed that the length of spacer has significant effects on the LC phase behavior of polymers. For PMTS and PMT2 S, they displayed the columnar phase developed by the Tp moieties and the main chain as a whole due to the strong coupling effect of the Tp moieties and the main chain. For the PMT3 S, PMT4 S and PMT6 S, they formed the symmetry hexagonal columnar(ΦH) phase owing to the decoupling effect. All of these indicated that the "decoupling effect" or "coupling effect" depended on the length of spacers, leading to the different LC phase formation mechanism.     

Study on thermal degradation mechanisms of comb polyacrylates containing long fluorocarbon side chains by TG/FTIR

Thermal degradation of two series of polyacrylates containing long fluorocarbon chains [abbr.: PF_nA {HCF₂(CF₂)_n−1  CH₂ O C(O) , n = 4, 6, 8, 10} and abbr.: PFF_nEA {CF₃(CF₂)_n−1  CH₂CH₂ O C(O) , n = 6, 8, 10}] was investigated by TG /FTIR. Thermal degradation behavior of polymers changed depending on the type of tie groups, which link the fluorocarbon chains to the main chain, and also on the length of fluorocarbon chains. It was clarified that the apparent activation energies (ΔE_a ) of PF_nA series obtained by Ozawa's method varied in the order of PF₄A > PF₆A > PF₈A > PF₁₀A, while those of PFF_nEA series having tie group of  CH₂ CH₂ O C(O) were almost constant. The results for PF_nA series (tie group:  CH₂ O C(O) ) are attributable to the shield effect of long fluorocarbon chains on the back‐biting reaction in the thermal degradation of comb polymers rather than the change of C C bond dissociation energy in the main chain. It was found that TG curves of PFF_nEA series were shifted to the lower temperature region than those of PF_nA. This result can be attributable to the scission of side groups followed by the evaporation of fluorocarbon compounds and carbon dioxide. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2794–2803, 2000     

Star‐shaped polymers having side chain poss groups for solid polymer electrolytes; synthesis,thermal behavior,dimensional stability,and ionic conductivity

A series of organic/inorganic hybrid star‐shaped polymers were synthesized by atom transfer radical polymerization using 3‐(3,5,7,9,11,13,15‐heptacyclohexyl‐pentacyclo[9.5.1.1^3,9.1^5,15.1^7,13]‐octasiloxane‐1‐yl)propyl methacrylate (MA‐POSS) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) as monomers and octakis(2‐bromo‐2‐methylpropionoxypropyldimethylsiloxy)octasilsesquioxane as an initiator. Star‐shaped polymers with methyl methacrylate (MMA) and PEGMA moieties were also prepared for comparison purposes. Dimensionally stable freestanding film could be obtained from the hybrid star‐shaped polymer containing 26 wt % of MA‐POSS moieties although its glass transition temperature is very low, ?60.9 °C. As a result, the hybrid star‐shaped polymer electrolyte containing lithium bis(trifluoromethanesulfonyl)imide showed ionic conductivities (1.75 × 10^?5 S/cm at 30 °C), which were two orders of magnitude higher than those of the star‐shaped polymer electrolyte with MMA moieties. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Chain structure and thermal behavior of reactive blends of PET/LCP with bis(2-oxazoline)

The sequence structure and thermal behavior of reactive blends of poly(ethylene terephthalate) (PET) with the liquid crystalline copolyester 60 PHB/PET containing 60 mol % of p-hydroxybenzoic acid (PHB) with addition of bis(2-oxazoline) (BOZ) were studied in detail. ¹H NMR results indicate that both the number average sequence length of PET and PHB segments (L _PET and L _PHB) decrease with increasing mixing time and temperature via transesterification between PET and LCP. The transesterification is promoted in the presence of BOZ. As a consequence, the sequence structure and in turn the crystallization both from the glassy and the melt state and the melting behavior are markedly affected.     

Influence of liquid crystalline polymer and recycled PET as minor blending components on rheological behavior,morphology, and thermal properties of thermoplastic blends

In this study, the potential of recycled poly(ethylene terepthalate) (rPET) as a well‐defined reinforcing material for the in situ microfibrillar‐reinforced composite (iMFC) was investigated in comparison with that of liquid crystalline polymer (LCP). Each dispersed phase (LCP or rPET) was melt blended with high density polyethylene (PE) by using extrusion process. The rheological behavior, morphology, and the thermal stability of LCP/PE and rPET/PE blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of LCP or rPET into PE significantly improved the processability. A potential of rPET as a processing lubricant by bringing down the melt viscosity of the blend system was as good as LCP. The elongated LCP domains were clearly observed in as‐extruded strand. Although the viscosity ratio of the rPET/PE system was lower than that of the LCP/PE blend system, most rPET domains appeared as small droplets. An addition of LCP and rPET into the PE matrix improved the thermal resistance significantly in air but not in nitrogen. The obtained results suggested the high potential of rPET as a processing aid and good thermally resistant material similar to LCP. Copyright © 2009 John Wiley & Sons, Ltd.     

Toughening of highly crosslinked epoxy resins by reactive blending with bisphenol A polycarbonate. II. Yield and fracture behavior

The yield and fracture behavior of highly crosslinked epoxy resin modified by a reactive blending process carried out in the presence of bisphenol A polycarbonate has been studied. It was found that the fracture toughness of this blend system increases markedly with increasing PC content in the blend. Scanning electron microscopy of the fractured surfaces indicated a crack blunting mechanism as the main source of energy dissipation in the various investigated blend compositions. No evidence of phase separation of the minor component during the curing and postcuring steps was observed. The yield data were correlated with the fracture toughness data to evaluate the extent of crack-tip blunting. © 1994 John Wiley & Sons, Inc.     

Structure and dynamics of rodlike polyester with long n-alkyl side chains over a wide range of temperatures by solid state C NMR

Solid state ¹³C NMR experiments on poly(p-biphenylene terephthalate) with long n-dodecyl side chains have been carried out over a wide range of temperatures, in order to elucidate conformational and dynamical behavior of the polyester in the crystalline state and thermotropic liquid crystalline state. From these experimental results, it is found that at temperatures from room temperature to 80 °C the n-alkyl side chains take both of the immobile and the mobile regions, and at temperatures above 120 °C take only the mobile region. In the immobile region the n-alkyl side chains are in the all-trans zigzag conformation and in the mobile state are undergoing fast exchange between the trans and gauche conformations. On the other hand, the terephthalate moiety of the main chain undergoes rotational motion after the melt of n-alkyl side chains as the temperature is increased.     

Supramolecular assembly of H‐bonded side‐chain polymers containing conjugated pyridyl H‐acceptor pendants and various low‐band‐gap H‐donor dyes bearing cyanoacrylic acid groups for organic solar cell applications

Novel supramolecular side‐chain polymers were constructed by complexation of proton acceptor (H‐acceptor) polymers, i.e., side‐chain conjugated polymers P1–P2 containing pyridyl pendants, with low‐band‐gap proton donor (H‐donor) dyes S1–S4 (bearing terminal cyanoacrylic acids) in a proper molar ratio. Besides unique mesomorphic properties confirmed by DSC and XRD results, the H‐bonds of supramolecular side‐chain structures formed by pyridyl H‐acceptors and cyanoacrylic acid H‐donors were also confirmed by FTIR measurements. H‐donor dyes S1–S4 in solid films exhibited broad absorption peaks located in the range of 471–490 nm with optical band‐gaps of 1.99–2.14 eV. Furthermore, H‐bonded polymer complexes P1/S1–P1/S4 and P2/S1–P2/S4 exhibited broad absorption peaks in the range of 440–462 nm with optical band‐gaps of 2.11–2.25 eV. Under 100 mW/cm² of AM 1.5 white‐light illumination, the bulk heterojunction polymer solar cell (PSC) devices containing an active layer of H‐bonded polymer complexes P1/S1–P1/S4 and P2/S1–P2/S4 (as electron donors) mixed with [6,6]‐phenyl C₆₁ butyric acid methyl ester (i.e., PCBM, as an electron acceptor) in the weight ratio of 1:1 were investigated. The PSC device containing H‐bonded polymer complex P1/S3 mixed with PCBM (1:1 w/w) gave the best preliminary result with an overall power conversion efficiency (PCE) of 0.50%, a short‐circuit current of 3.17 mA/cm², an open‐circuit voltage of 0.47 V, and a fill factor of 34%. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5998–6013, 2009     

Copolymers of 2,5‐bis[(4‐methoxyphenyl) oxycarbonyl]styrene with styrene and methyl methacrylate: Synthesis,monomer reactivity ratios,thermal properties,and liquid crystalline behavior

Copolymers of a liquid crystalline monomer, 2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene (MPCS), with St and MMA were prepared by free radical polymerization at low conversion in chlorobenzene with 2,2′‐azobisisobutyronitrile (AIBN) as initiator. The copolymers of poly(MPCS‐co‐St) and poly(MPCS‐co‐MMA) were characterized by ¹H NMR and GPC. The monomer reactivity ratios were determined by using the extended Kelen–Tudos (EKT) method. Structural parameters of the copolymers were obtained from the possibility statistics and monomer reactivity ratios. The influence of MPCS content in copolymers on the glass transition temperatures of copolymers was investigated by DSC. The thermal stabilities of the two copolymer systems increased with an increase of the molar fraction of MPCS in the copolymers. The liquid crystalline behavior of the copolymers was also investigated using DSC and POM. The results revealed that the copolymers with high MPCS molar contents exhibited liquid crystalline behaviors. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2666–2674, 2005     

Effect of methyl groups on the thermal properties of polyesters from methyl substituted 1,4-butanediols and 4,4′-biphenyldicarboxylic acid

Results are reported on the effect of lateral methyl groups on the thermal properties of a series of polyesters prepared from diethyl 4,4′-biphenyldicarboxylate and various methyl substituted 1,4-butanediols. The diols were 1,4-butanediol; 2-methyl-1,4-butanediol; 2,2-dimethyl-1,4-butanediol; 2,3-dimethyl-1,4-butanediol; 2,2,3-trimethyl-1,4-butanediol; and 2,2,3,3-tetramethyl-1,4-butanediol. Apart from the tetramethyl derivatve, the transition temperatures of the methyl substituted polyesters were lower with respect of the unsubstituted polyester. On the basis of polarized photomicrographs, a smectic A mesophase was found for the unsubstituted polyester, whereas a nematic mesophase was observed for the 2-methyl substituted polyster. The 2,2-dimethyl, 2,3-dimethyl, and the 2,2,3-trimethyl substituted polyesters showed no liquid crystalline behavior. The 2,2,3,3-tetramethyl derivative displayed a birefringent melt phase although the DSC measurements were not unambiguous. A copolyester based on diethyl 4,4′-biphenyldicarboxylate, 1,4-butanediol, and 2,2,3,3-tetramethyl-1,4-butanediol showed a broad nematic mesophase. Further evidence for the nematic mesophase of this copolyester and the 2-methyl substituted polyester was provided by dynamic rheological experiments. Based on thermogravimetric analysis, it was concluded that the thermal stability was affected only when four methyl side groups were present in the spacer. © 1995 John Wiley & Sons, Inc.