Biodegradable shape memory polyurethanes with controllable trigger temperature

A series of random copolymers(PCLAs) were synthesized by ring-opening polymerization of D,L-lactide(LA)and ε-caprolactone(CL) with different molar ratios. PCLA based polyurethanes(PCLAUs) were obtained by chain-extending of PCLA and polytetramethylene ether(PTMEG) with hexamethylene diisocyanate(HDI). All the PCLAUs exhibit good shape memory properties with high shape fixity ratios above 98% and shape recovery ratios above 82% in the first cycle and 91% in the second cycle. PCLAUs with less CL content show faster recovery speed and PCLAUs with more CL content show higher shape recovery ratio. The trigger temperature can be tuned or controlled around body temperature by adjusting the molar ratio of LA to CL. The PCLAUs have potential applications in implant biomedical devices, especially for minimally invasive deployable devices.     

STUDIES ON GRAFT COPOLYMERIZATION OF DL—LACTIDE ON CORN STARCH AND BIODEGRADABILITY OF THE COPOLYMERS

The starch/D,L-lactide graft copolymers were synthesized by reacting D,L-lactide with corn starch in N,N-dimethylacetamide(DMAM)in the presence of triethylamine(NEt3)and anhydrous lithium chloride.The effect of reaction time and the molar ratio of D,L-lactide to glucose structural unit of starch on monomer conversion(C%),graft(G%)and graft efficiency(GE%)were studied,The C%,G%and GE% could approach 37.3% 179.7%and 68.0%,respectively when the molar ratio of D,L-lactide to glucose structuralunit of starch is 10:1 and the graft copolymerization was carried out at 80-85℃ for 4hr under nitrogen atmosphere.The Fourier transforms infra-red (FTIR) spectroscopy.differential scanning calorimetry(DSC)and X_ray diffraction (XRD) spectroscopy were used in order to characterize the graft copolymers.FTIR spectra show that absorption band at 1740cm^-1 confirmed the formation of ester bond,indicating the starch /D,L-lactide graft copolymers were produced,the DSC characteristic results show the melting temperature of the graft copolymer were elevated slightly as the molar ratio of D,L-lactide to glucose structural units of starch increased and the X-ray diffraction spectra show the synthesized graft copolymers were amorphous.The degradability of graft copolymer was tested with the aid of acid,alkali and microbe such as bacillus subtilis and staphylococcus aureus.The results of water rsistance show the graft copolymer produced can be used as a component of impermeable coating for cardboard.     

L-Lactide Homopolymerization and Copolymerization with ε-Caprolactone by Tetrahydrosalen Stabilized Yttrium Borohydride Complex

L-lactide（LLA） homopolymerization and copolymerization with ε-caprolactone（CL） in toluene initiated by tetrahydrosalen-supported yttrium borohydride complex were systematically investigated. A possible mechanism of LLA homopolymerization was proposed according to the 1H-NMR result. In addition, PCL-b-PLLA copolymers were synthesized by sequential addition of monomers and their structure was characterized by GPC, 1H-NMR and 13C-NMR.     

Synthesis and Characterization of ABBA Block Copolymer of Glycolide and ε-Caprolactone

A biodegradable ABBA block copolymer was synthesized via the ring-opening co-polymerization of ε-Scaprolactone (CL, B) and glycolide (A) by means of step polymerization in the presence of ethylene glycol as an initiator and stannous octanoate as a catalyst at 110 ℃ for 48 h. The molecular length of the PCL prepolymer(BB) could be adjusted by controlling the molar ratio of the ethylene glycol initiator to ε-caprolactone monomer. The structure and the composition of the block copolymer were determined by the weight ratio of the monomer glycolide (A) to PCL pre-polymer(BB). The block copolymers were characterized by ^1H NMR, GPC, DSC and X-ray. The results confirm the successful synthesis of an ABBA block copolymer.     

Copolymer of lactide and ε-caprolactone catalyzed by bimetallic Schiff base aluminum complexes

A series of copolymers of lactide(LA) and e-caprolactone(ε-CL) with different monomer feed ratios were achieved using three kinds of bimetallic Schiff aluminum complexes as catalysts. The ratios of LA and ε-CL units in different copolymers and the average segments length were determined by NMR analysis. The comparative kinetic study of L-LA/ε-CL and rac-LA/ε-CL copolymerization systems showed that the polymerization rate of LA was faster than ε-CL, and L-LA showed polymerization rate slightly faster than rac-LA. It was inferred that the copolymers achieved by these complexes were gradient copolymers with gradual change in distribution of LA and e-CL units. The thermal properties of these copolymers were characterized by DSC analysis, which showed that the glass transition temperature(Tg) of these copolymers changed regularly according to the pro-portion change of two structural units.     

COPOLYMERIZATION PROCESS OF TRIPHENYLMETHYL METHACRYLATE AND MMA WITH CHIRAL ANIONIC COMPLEX INITIATOR

The copolymerization process of triphenylmethyl methacrylate (TrMA) and methylmethacrylate (MMA) using chiral anionic complex initiator (-) SP-FlLi (Scheme 1) has beenstudied in toluene and THF, respectively. The copolymer obtained in toluene possessed muchhigher specific rotation than that in THF. These copolymers have shown a tendency to a random and a like alternating structure, respectively.     

MISCIBILITY IN COPOLYMER/HOMOPOLYMER BLENDS

In order to study the miscibility of a copolymer with its corresponding homopolymers, varieties of multicomponent polymers including simple graft, muhibranch, diblock, triblock and four-arm block copolymers and so-called ABCPs were synthesized and characterized. The morphologies of the blends comprising the copolymers and the corresponding homopolymers were examined by electron microscopy. It is concluded that besides molecular weight, architecture of a copolypaers has apparent effect on the miscibility, i.e. the more complex is molecular architecture, the greater is conformation restriction in microdomain formation and the less is solubility of homopolymer in corresponding domains. In addition, a density gradient model is suggested for describing the segment distribution of the bound and free chains in block-homopolymer systems. Using this model, Helfand's theory is extended to the blends of copolymer and homopolymer predicting the miscibility which is in good agreement with the experimental results.     

Copolymerization of PO/CO2 and Lactide by a Dinuclear Salen-Cr(Ⅲ) Complex: Gradient and Random Copolymers with Modificable Microstructure

Copolymerization of propylene oxide(PO)/carbon dioxide(CO₂) and lactide(LA) is achievable to form new copolymers, combining the advantages of both poly(propylene carbonate)(PPC) and polylactide(PLA). In this study, we designed a dinuclear Salen-Cr(Ⅲ) complex, which showed higher efficiency for copolymerization of PO/CO₂ and LA than that of mononuclear Salen-Cr(Ⅲ) complex. Besides, we successfully obtained gradient and random copolymers of PPC-PLA in one pot. Furthermore, by...     

The copolymerization of L-lactide and ε-caprolactone using magnesium octoate as a catalyst

Copolymerizations of L-lactide （L-LA） and ε-caprolactone （ε-CL） were conducted in bulk using magnesium octoate as a catalyst. The reactivity ratios of L-LA and ε-CL were determined to be rL=23 and rc=0.22, respectively. The sequence analyses of the copolymers were performed on ^13C NMR. An increase in the reaction temperature enhances the role of transesterification and the extent of randomness.     

TUNED MECHANICAL PROPERTIES ACHIEVED BY VARYING POLYMER STRUCTURE — KNOWLEDGE THAT GENERATES NEW MATERIALS FOR TISSUE ENGINEERING

By changing both the monomer composition and the polymer structure, we have varied the mechanical properties of resorbable polymers. The polymers were synthesized by ring-opening polymerization using L-lactide （LLA）, ε-caprolactone （εCL）, trimethylene carbonate （TMC） and 1,5-dioxepan-2-one （DXO） as monomers. Well-defined triblock copolymers, microblock copolymers and networks have been evaluated, and comparisons between them show that it is possible to tune the mechanical properties. Triblock copolymers with an amorphous middle block of poly（1,5-dioxepan-2- one） （PDXO） and semi-crystalline end-blocks of poly（ε-caprolactone） （PCL） were stronger and had a higher strain at break than triblock copolymers with poly（L-lactide） （PLLA） as end-blocks. Polymers with both DXO and TMC in the amorphous middle-block and PLLA as end-blocks showed a lower stress at break, but the material gained elasticity, a property which is very valuable in tissue engineering. Mechanical properties of networks, synthesized by a novel method, containing PDXO and PCL are also presented. Although it is difficult to compare them with the uncross-linked polymers, this is an additional way to modify and widen the properties.     

Synthesis and characterization of a novel polymer electrolyte based on acrylonitrile/N-[4-(aminosulfonyl)phenyl]acrylamide copolymers

<正>Acrylonitrile/N-[4-(aminosulfonyl)phenyl]acrylamide(AN/ASPAA) copolymers were synthesized and used as a host of lithium ion conducting electrolytes.The composition,molecular weight and molecular weight distribution of AN/ASPAA copolymers were determined,and the influence of copolymer composition on the glass temperature of AN/ASPAA copolymers and the ion conductivity of electrolytes were investigated.The molecular weights of AN/ASPAA copolymers were lower than those of AN and ASPAA homopolymers due to the cross-termination reaction.The glass temperatures of AN/ASPAA copolymers increased as the molar fraction of ASPAA units in copolymers increased.The lithium ion conductivities of the polymer electrolytes increased initially as the molar fraction of ASPAA units in copolymers increased,and a maximum conductivity was achieved when the molar fraction of ASPAA in the copolymer was 16.8%.     

Self-assembly of linear rod-coil multiblock copolymers

The self-assembly of the linear rod-coil multiblock copolymers is studied by applying self-consistent-field lattice techniques in a three-dimensional (3D) space. Compared to the copolymer with one rod, the copolymer with more rods (mrod≥2) exhibits rich order-order phase transitions with increasing temperature, where the ordered morphology changes from strips to perforated lamellae and finally to lamellae. In addition, taking the copolymer with mrod = 2 as a representative, we further study the effects of the volume fractions of the rods, the spacer coils and the end coils on the phase behaviors respectively, by which the detailed self-assembled mechanism of the linear rod-coil multiblock copolymers is revealed. Our results are expected to provide guidance for the design of the rod-coil materials.     

Synthesis of graft copolymers with polyisobutylene branch chains

<正>The copolymerization of 4-vinylbenzyl chloride(VBC) and vinyl acetate(VAC) was carried out in toluene at 75℃via radical polymerization using 2,2'-azo-bis-(isobutyronitrile)(AIBN) as an initiator.The random copolymers of poly(4-vinylbenzyl chloride-co-vinyl acetate)(P(VBC-co-VAC)) with number average molecular weight(M_n) from 2000 to 6900,relatively narrow molecular weight distribution(MWD,M_w/M_n ca.2.0) and with different copolymer composition of 4-vinylbenzyl chloride(VBC) from 17 mol%to 62 mol%could be obtained.The P(VBC-co-VAC) copolymers with an average number of 7 to 13 initiating sites of benzyl chloride per macromolecule could be used for the cationic polymerization of isobutylene(IB).The cationic polymerizations of IB were further conducted by using P(VBC-co-VAC) copolymers as macroinitiators in conjunction with TiCl_4 at -40℃in CH_2Cl_2.The effects of VBC/TiCl_4(molar ratio) on monomer conversion,M_n and MWD of the resultant copolymers were investigated under 3 sets of conditions.It is found that P(VBC-co-VAC)-g-PIB copolymers with relatively narrow MWD(M_w/M_n ca.2.0) and with terminal tert-chlorine functional groups in branched PIB chains could be successfully synthesized when VBC/TiCl_4(molar ratio) was set in the range from 0.10 to 1.12.The unimodal GPC curve of the P(VBC-co-VAC)-g-PIB copolymers by RI detector was almost in harmony with the GPC curve by UV detector.The TEM image of the P(VBC-co-VAC)-g-PIB copolymer stained by RuO indicated that the copolymer formed a two-phase morphology with P(VBC-co-VAC)-rich domains of 20-100 nm in size tethered by PIB branch segments.     

Detection of free surface composition and molecular-level structural development of styrene(S)/butadiene(B) block copolymer films during a solution-to-film process

The surface chemical structure development in solution-cast styrene(S)/butadiene(B) block copolymer films as a function of solvent evaporation time was investigated using sum frequency generation vibrational spectroscopy(SFG).The surface structure formation of the styrene(S)/butadien(B) block copolymer(30 wt% PS) films during the solution-to-film process was found to be controlled mainly by dynamic factors,such as the mobility of the PB block in solution.For SB diblock copolymers,a pure PB surface layer was formed only when the film was cast by dilute toluene solution.With increasing concentration of casting solution,PB and PS components were found to coexist on the film surface,and the morphology of the PB component on the film surface changed from cylindrical rods to spheres.For SBS triblock copolymers,a small amount of PS component existed on the surface even if the film was cast by 1.0 wt% toluene solution.In addition,PS components at the outermost layer of the film increased and the length of PB cylindrical rods on the surface decreased with increasing concentration of casting solution.     

Flexible Gradient Poly(ether-ester) from the Copolymerization of Epoxides and ε-Caprolactone Mediated by a Hetero-bimetallic Complex

Copolymerization is a commonly employed method for optimizing the properties of polymer materials. Incorporating ether segments into polyesters main chain to obtain polyether-polyester copolymers is an effective strategy to realize the integration of multiple properties of polyester and polyether, and to develop more high-performance, multi-purpose polymer materials. Herein, the synthesis of poly(ether-ester)s is accessible by employing the biphenyl-linked heterodinuclear salen Cr-Al complex in the presence of PPNCl for the copolymerization of epoxides and ε-caprolactone(CL). Monitoring the copolymerization process reveals that catalyst 1 exhibited good performance for the copolymerization of epoxides and CL, affording copolymers with a gradient sequence structure. The dynamic thermomechanical analysis(DMA) study indicates the obtained poly(ether-ester)s possess enhanced flexibility compared with the block copolymers or blend of PPO and PCL homopolymers with the same ratio. This study provides a theoretical basis for the preparation of high-performance polymer materials.     

Rapid synthesis of biodegradable poly(epsilon-caprolactone-co-p-dioxanone) random copolymers under microwave irradiation

<正>Biodegradable poly(epsilon-caprolactone-co-p-dioxanone)(PCDO) random copolymers have been synthesized by ring-opening polymerization of epsilon-caprolactone(CL) and p-dioxanone(PDO) under microwave irradiation.The effects of irradiation time and different CL/PDO molar feed ratios on the microwave-assisted ring-opening polymerization(MROP) of PCDO have been discussed.The resultant products were characterized by ~1H NMR,GPC and DSC.It was found that the polymerization was completed within 20 min at 140℃.In the presence of different CL/PDO molar feed ratios,the conversions of both monomers were kept relatively constant.DSC sturdy suggested that with increasing the content of PDO in the copolymers,the crystalline degree of the copolymers decreased gradually.It is believed to be a promising biodegradable material.     

PHOTOPHYSICAL STUDIES OF POLYMER NETWORKS 1. Fluorescence Characteristics of Styrene/p-Divinylbenzene Crosslinked Polymers

Fluorescence properties of a series of styrene/p-divinylbenzene (St/p-DVB) copolymer beads were investigated by steady-state fluorescence spectra. In addition to the fluorescence of the phenyl ring excimer, a new emission band at ca 395nm appears when p-DVB content in feed is higher than 13%(wt). The intensity of this new emission was found to change with pDVB content and to decrease with swollen beads. The origin of this new emission is considered to be a multi-ring excimer formation.     

Preparation of Nano-porous Materials( Ⅱ） by Cross-linking of Amphiphilic Self-assemblies

Amphiphilic block copolymers can exhibit rich and complex morphologies in aqueous solutions but these structures are usually delicate,easily disturbed by composition change or temperature change.In this work,the use of different methods to cross-link block copolymer self-assemblies in the presence of a selective solvent and to stabilize the structures is reviewed.In addition,the cross-linking reaction kinetics of block copolymer amphiphilic self-assemblies is briefly discussed.     

COMPUTER SIMULATION OF MISCIBILITY AND SELF-ASSEMBLY STRUCTURE FOR POLYMER-CONTAINING SYSTEMS WITH SPECIAL INTERACTIONS

The miscibility and structure of A-B copolymer/C homopolymer blends with special interactions were studied by aMonte Carlo simulation in two dimensions. The interaction between segment A and segment C was repulsive, whereas it wasattractive between segment B and segment C. In order to study the effect of copolymer chain structure on the morphologyand structure of A-B copolymer/C homopolymer blends, the alternating, random and block A-B copolymers were introducedinto the blends, respectively. The simulation results indicated that the miscibility of A-B block copolymer/C homopolymerblends depended on the chain structure of the A-B copolymer. Compared with alternating or random copolymer, the blockcopolymer, especially the diblock copolymer, could lead to a poor miscibility of A-B copolymer/C homopolymer blends.Moreover, for diblock A-B copolymer/C homopolymer blends, obvious self-organized core-shell smicture was observed inthe segment B composition region from 20% to 60%. However if diblock copolymer composition in the blends is less than40%, obvious self-organized core-shell structure could be formed in the B-segment component region from 10 to 90%.Furthermore, computer statistical analysis for the simulation results showed that the core sizes tended to increasecontinuously and their distribution became wider with decreasing B-segment component.     

“SERGEANTS AND SOLDIERS RULE” IN HELICAL SUBSTITUTED-ACETYLENE COPOLYMER EMULSIONS

The "sergeants and soldiers rule" occurring in helical copolymer emulsions derived from an achiral monomer (M1) and a chiral monomer (M2) was observed. TEM, GPC, and 1H-NMR techniques in combination demonstrate the formation of nanoparticles constituted by the copolymers. CD and UV-Vis spectra show the (co)polymer chains in the nanoparticles adopt helical structures of a predominant helicity, and the copolymers follow the "sergeants and soldiers rule" in forming helical structure.