Crystallinity in quasi-alternating cycloolefin copolymers: Overcoming brittleness

Cycloolefin copolymers (COCs, which are produced via ethylene/cycloolefin copolymerization) and cycloolefin polymers (COPs, which are synthesized by a rather complicated two-step process via ring-opening metathesis polymerization and subsequent hydrogenation) are commercialized materials used especially widely in optical applications. Although a COP can be used after processing into a film, films made from conventional COCs are too brittle. Optical-grade COCs and COPs are generally known as amorphous polymers. By contrast, here, a quasi-alternating ethylene/norbornene copolymer (norbornene content 56 mol%), prepared from a constrained-geometry Hf complex, shows some melting (T_m) signals in a broad temperature range (150–200°C) in the first heating scan of differential scanning calorimetry (DSC) when the samples are prepared by precipitation from a toluene solution. In the second heating scan, only glass transition (T_g) signals are observed at ~140°C with disappearance of T_m signals. The quasi-alternating ethylene/norbornene copolymer has better mechanical properties (greater elongation at break) than random congeners, which do not show any melting signal, though elongation at break is still inferior to that of the COP which shows the melting signal in the first heating scan of DSC. The enhanced mechanical properties of the quasi-alternating ethylene/norbornene copolymer and commercial-grade COP may be ascribed to semicrystallinity observed in the first heating scan.     

VDF/TFE/PMVE三元共聚物的结构与性能研究

控制不同单体的起始组成合成了一系列偏氟乙烯 (VDF) 四氟乙烯 (TFE) 全氟甲基乙烯基醚 (PMVE)三元共聚物 ,通过1 9F NMR测定了这类三元共聚物的组成 ,结果与按竞聚率的计算结果吻合 .进一步分别用DSC和WAXD表征了玻璃化温度和结晶度 ,实验结果发现用这类三元共聚物制成的硫化胶的性能与其组成和微观结构密切相关     

Synthesis of gradient copolymers with simultaneously tailor‐made chain composition distribution and glass transition temperature by semibatch ATRP: From modeling to application

Recent studies have demonstrated that gradient copolymers exhibit unique thermal properties. Although these properties can be determined by copolymer composition, other factors such as chain and sequence lengths and their distributions can also influence them. Accordingly, the synthesis of gradient copolymers requires simultaneously tailor‐made chain structure and thermal properties. In this work, we carried out a systematic study on the preparation of poly(methyl methacrylate‐grad‐2‐hydroxyethyl methacrylate) [poly(MMA‐grad‐HEMA)] with synchronously tailor‐made chain composition distribution and glass transition temperature (T_g) through semibatch atom transfer radical polymerization. First, a comprehensive model for simultaneously predicting gradient copolymer microstructure and T_g was presented using the concept of pseudo‐kinetic rate coefficients and Johnston equation. The model was validated by comparing simulation results with the classical reference data. Furthermore, the model was used to guide the experimental synthesis of the poly(MMA‐grad‐HEMA) gradient copolymers potentially as excellent damping material. The thermal properties of these gradient copolymer samples were evaluated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

蓖麻油与乳酸的共聚物合成与表征

用熔融聚合法合成了一种蓖麻油和乳酸的共聚物.以丁二酸酐作为共聚体系的引发剂和封端剂,制得端羧基共聚物P(LA-CO)-COOH.研究了反应条件对共聚物分子量的影响,通过核磁共振表征了共聚物的结构.DSC和TG研究表明,蓖麻油链段的引入破坏了聚乳酸的结晶性,提高了共聚物的热稳定性.     

Properties of well‐defined alternating and random copolymers of methacrylates and styrene prepared by controlled/living radical polymerization

The physical properties of well‐defined alternating copolymers poly(methyl methacrylate‐alt‐styrene) and poly(n‐butyl methacrylate‐alt‐styrene), prepared by reversible addition–fragmentation chain transfer polymerization in the presence of Lewis acids, were investigated with differential scanning calorimetry, wide‐angle X‐ray scattering, and dynamic mechanical measurements. The properties were compared with those of random copolymers of the same overall composition and the corresponding homopolymers. Wide‐angle X‐ray scattering data showed that the alternating copolymers possessed a more regular comonomer sequence than the random copolymers. The thermomechanical properties of alternating copolymers and random copolymers were quite similar and typical for amorphous polymers, but in one of the cases studied the glass‐transition temperature for alternating copolymer was remarkably higher than for the random copolymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3440–3446, 2005     

Analysis of glass transition and relaxation processes of low molecular weight polystyrene-b-polyisoprene diblock copolymers

The objective of this study is to analyze the glass transition temperature and relaxation processes of low molecular weight polystyrene-block-polyisoprene diblock copolymers with different compositions, synthesized via anionic polymerization. Thermal properties were investigated by differential scanning calorimetry and dynamic-mechanical thermal analysis, while the morphologies at room temperature were investigated by transmission electron microscopy and small-angle X-ray scattering. The χN values indicate that the diblock copolymers lie near the weak segregation regime. Three different experimental techniques were applied to determine the dynamic properties, i.e., linear viscoelastic shear oscillations, creep recovery experiments, and dielectric spectroscopy. The rheological experiments were performed above the order–disorder transition temperature where the diblock copolymers behave like a Maxwell fluid. Our results indicate that the presence of the polyisoprene segments strongly influences the monomeric friction coefficient and the tendency to form entanglements above the order–disorder temperature. Consequently, the zero-shear rate viscosity of a diblock copolymer is much lower than the zero-shear rate viscosity of the neat polystyrene block (the polystyrene precursor of the polymerization procedure). Dielectric spectroscopy enables the analysis of relaxation processes below the glass transition of the polystyrene microphase. Frequency sweeps indicate the dynamic glass transition of the polyisoprene blocks, which are partly mixed with the polystyrene blocks, which are always the majority component in the block copolymers of this study.     

Potential Biodegradable Implants from ϵ-Caprolactone and D,L-Lactide Copolymers: Synthesis,Properties, and In Vivo Degradation

Random copolymers of ?-caprolactone (CL) and D, L-lactide (DLLA) were synthesized by ring-opening polymerization using stannous octoate as catalyst. The effect of polymerization conditions, such as feeding dose, reaction temperature, polymerization time, and catalyst content on the properties of the copolymers was evaluated to prepare suitable copolymers with controlled properties for biodegradable implant applications. The results showed that the polymerization conditions influenced the thermal and mechanical properties of the copolymers strongly and controllable and tunable properties of random copolymers could be obtained by adjusting the copolymer compositions. The optimum reaction conditions to prepare the CL-DLLA copolymers for implant applications are 30–87 mol.% DLLA content in feeding dose, 110°C reaction temperature, and 24 h polymerization time. The results of in vivo implantation revealed the excellent degradability of CL-DLLA copolymers. Copolymers of CL and DLLA with different compositions and properties would be suitable for the application of biodegradable implants.     

Volume shrinkage and abrasive wear properties of crosslinked Poly(ester-urethane-acrylate)/MMA copolymer: Effect of chain length

The current study deals with the preparation of novel crosslink transparent poly(ester-urethane-acrylate)/methyl methacrylate (TPEUMA) copolymers and the effect of hydroxyl terminated aromatic polyester (PEs) was also investigated. The properties of TPEUMA were investigated in terms of double bond concentration, polymerization shrinkage, abrasive wear analysis and chemical resistance. The volume shrinkage decreased due to the significant reduction in the concentration of double bonds. The first two effects reflect in lowering the abrasive wear resistance properties at room temperature, while the larger chain length between crosslink decreases the hardness. Decrease in polymerization shrinkage shows more condensed microstructure which was revealed by the abrasive wear rate of TPEUMAs due to hydrogen bonding near to crosslink point. Increase in the chain length of PEs, decreases the glass transition temperature of TPEUMA copolymer which results in loose microstructure. Worn surface were studied using scanning electron microscope to give insight on the wear mechanism of TPEUMA crosslink. It can be suggested from the present study that this copolymer can be used for a broad range of optical applications.     

Structure and property relationships in ethylene–vinyl acetate copolymers

The effects of vinyl acetate content on crystallinity of ethylene–vinyl acetate (E/VA) copolymers were investigated by x-ray diffraction and differential thermal analysis (DTA). The values of these parameters obtained from DTA were found to agree quantitatively with data calculated from x-ray, probability equations, and copolymer theory. The melting points of the crystalline copolymers, and the molar amounts of vinyl acetate to produce a completely amorphous rubber corresponds exactly to that predicted by the Flory theory. The random character expected in E/VA copolymers is thereby confirmed. The physical properties of E/VA copolymers of all ranges of compositions and crystallinity were determined. Depending directly upon vinyl acetate content, the copolymers changed progressively from highly crystalline polyethylene to semicrystalline polyethylene, a completely amorphous rubber, a soft plastic with a glass transition near room temperature. Properties which were correlated with copolymer composition include: crystallinity, melting point, density, modulus, tensile strength, glass transition, and solubility. Finally, the effect on crystallinity and physical properties of replacing the acetoxy group in E/VA with the smaller, highly polar hydroxyl group (ethylene—vinyl alcohol copolymer) was also investigated.     

N-苯基马来酰亚胺/对氯甲基苯乙烯活性可控超支化交替共聚合的研究

采用核磁共振氢谱, 研究了N-苯基马来酰亚胺(NPMI)与对氯甲基苯乙烯(PCMS)在氘代氯仿中的络合性能. 以PCMS作为引发剂单体, 通过原子转移自由基聚合(ATRP)引发NPMI-PCMS电子转移络合物(CTC)进行活性可控超支化共聚合. 考察了单体初始摩尔分数对共聚物组成和其玻璃化转变温度的影响, 用Kelen-Tudos法计算得到两种单体的竞聚率分别为 r_NPMI＝0.11和r_PCMS＝0.25. 结果表明, 当单体配比f_NPMI＝0.4～0.7时, 共聚物具有交替结构, 其耐热性随着NPMI含量的增加而提高. 此外还考察了溶剂、聚合温度等对共聚合反应动力学的影响. 并进一步用所得超支化交替共聚物作为大分子引发剂, 引发甲基丙烯酸甲酯(MMA)聚合, 制得了多臂超支化接枝共聚物 poly(NPMI-co-PCMS)/poly(MMA).     

聚芳醚酮与液晶聚酯多嵌段共聚物的合成表征

近年来,以热塑性聚合物为基体,热致液晶聚合物(TLCP)作为增强剂的高分子原位复合材料由于其具有优异的机械性能和优良的成型加工性能,已引起各国工作者的普遍关注和极大兴趣．然而由于自聚集和相分离作用的影响,大部分液晶聚合物与通常的热塑性聚合物基体基本不相容或弱相容,这对于提高原位复合材料的力学性能不利．     

序列结构对苯乙烯/丁二烯共聚物热释电流峰的影响

本文研究聚合方式对苯乙烯/丁二烯共聚物热释电流峰(TSC)的影响。共聚物试样有三个电流峰(β、α和ρ峰)。实验结果表明:聚合方式对β峰(丁二烯局部运动)基本没有影响,但对α峰(丁二烯相的T_g转变)的位置有明显的影响,而且两步法试样有两个α峰;嵌段共聚物试样在高温还有一肩部(苯乙烯相的T_g转变),无规共聚试样没有肩部。由共聚物的序列结构能圆满解释TSC结果,而序列结构决定于聚合方式。因此,本工作将苯乙烯/丁二烯共聚物的序列结构与性能联系起来。     

Acenaphthylene Copolymers. II. Glass Transition Temperatures

Glass transition temperatures are reported for copolymers of acenaphthylene with the following comonomers: methyl meth-acrylate, styrene, maleic anhydride, diethyl maleate, N-vinyl-pyrrolidone, a-methylstyrene, and trans-stilbene. The data are discussed in terms of previously published treatments of the dependence of glass transition temperature on copolymer composition. The drop in glass transition temperature consequent upon incorporation of small quantities of comonomer is not related to the glass transition temperature of the corresponding homopolymer.     

共聚聚醚酯酰胺的多重转变及其相态结构

Segmented polyesteramides have been synthesized from N,N'-bis（p-carbomethoxybenzoy）butanediamine（T4T）as crystalline segments and mixture of poly（tetramethylene oxide）with the average molecular weight 1000（PTMO1000）and 1,5-pentanediol（PDO）as soft segments. The polymerization was carried out in the melt at 250℃ for 1-2 h while vacuum was applied. The chemical composition of the copolymer was measured by H1-NMR. The melting behavior of the copolymers was studied by the differential scanning calorimeter. The dynamic mechanical properties were investigated on injection moulded bars by means of dynamic mechanical analysis. It was found that the copolymers with more than 40% molar ratio PDO showed two glass transition temperatures and two melting temperatures. The glass transition temperatures are independent of composition,and thus two fully phaseseparated amorphous phases are present. The melting temperatures change with PDO content. The amount of PDO has an effect on both TmA and TmB . TmA is attributed to the lamella consisting of extended T4T segments,while TmB results from the much thicker lamella consisting of both extended T4T and PDO segments. It is also possible that some PDO is present in the interphase as adjacent re-entry groups. So the resultant copolymer shows that a complex system,two crystalline phases,two amorphous phases and an interphase are involved in the copolymer. The undercooling for these copolymers is small,which means that these segmented copolymers crystallize fast.     

Effect of the structure of latex particles on adhesion. Part I: Synthesis and characterization of structured latex particles of acrylic copolymers and their peel adhesion behavior

This is a series of articles that deals with fundamental aspects of the effects of the structure of latex particles of acrylic copolymers on their adhesion behavior. Specifically, relationship or analogy between rheological properties and adhesion performance of the acrylic copolymers was demonstrated. The first part of this series concerns the synthesis and characterization of latex particles with desired structures and compositions, and the experimental results of peel adhesion. The second part develops an analogy between the peel adhesion performance of the adhesives and rheological properties of the corresponding copolymers. The third part addresses the generalities and particularities of three major tests for adhesion: peeling, blistering, and spontaneous peeling. Three types of structured latex particles were synthesized by three different emulsion polymerization processes: the first type had a uniform composition over the entire particles with a glass transition temperature (T_g) varying between ?40°C and 0°C, depending upon the compositions of monomers involved in the copolymer; the second type was of core-shell structure. As for the third type, the composition of monomers varied gradually across the particle radii. The glass transition behavior and the dynamic mechanical properties in the solid state of the copolymers confirmed the structures of the corresponding latex particles. On the other hand, the peel adhesion performance of the films of these latex particles varied with the dynamic mechanical properties of the corresponding copolymers. This implies that a correlation could be found between the structure of the latex particles, dynamic mechanical properties in the solid state of the corresponding copolymers, and the peel adhesion performance of the adhesive films. ©1995 John Wiley & Sons, Inc.     

Chemical heterogeneity in emulsion copolymers of carboxylic monomers

Copolymer latices of butylacrylate (BA) with acrylic and methacrylic acid (AA and MAA) were prepared by batch type emulsion polymerization, and, for comparison, copolymers with identical monomer composition were prepared by batch type solution polymerization.The distribution of the carboxylic monomers in the latex particles and the serum was studied by density gradient and sedimentation experiments with the analytical ultracentrifuge. Dynamic mechanical measurements of films of these copolymers were used to determine the storage and loss moduli as a function of temperature. From these measurements the position and extension of the glass transition range on the temperature scale is obtained. For heterogeneous emulsion copolymers with two glass transition temperatures the distribution of the carboxylic monomer units in the different copolymer phases can be determined. Electron microscopy of ultra thin cross-sections of stained films gave further insight into the film morphology.The combination of the results obtained with the different methods gives rise to the following clues: In the BA/AA latices about 40% (by weight) of the total AA used in the recipe are found in the serum as a water soluble polymer, about 50% are found to increase the glass transition temperatureT _g of the bulk of the BA copolymer and, therefore, are thought to be incorporated into the interior of the latex particles, and the remaining 10% are, conclusively, located on the particle surface.In the BA/MAA latices no water soluble copolymer could be detected in the serum, about 90% of the MAA used is found in the bulk of the copolymer, and about 10% form a second hard phase on the surface of the latex particles.Dynamic mechanical measurements on the copolymer latex films show at least two phases with different glass transition temperatures: the bulk of the copolymer with a relatively low content of (M)AA units and a glass transition range at low temperatures, and a second (M)AA rich phase with a highT _g.The latter phase forms a honeycomb-like structure surrounding the packed latex particles. That results in a three-dimensional network of polymer with a highT _g extending throughout the latex film. In spite of the fact that this phase is built from a small fraction of the total copolymer only, it has a very pronounced influence on the performance behaviour of latex films.Dedicated to Professor Dr. R. Manecke on the occasion of his 70th birthday.     

Synthesis and characterization of random copolymers of (2,2-dimethyl-1,3-dioxolan-4-yl)methyl methacrylate and 2,3-dihydroxypropyl methacrylate

Poly[(2,2-dimethyl-1,3-dioxolan-4-yl)methyl methacrylate)] [poly(solketal methacrylate) (PSMA)] was synthesized by free radical polymerization. By partial hydrolysis of the acetal group, random copolymers of SMA with 2,3-dihydroxypropyl methacrylate (DHPMA) were synthesized whereas complete cleavage lead to poly(2,3-dihydroxypropyl methacrylate) (PDHPMA). The copolymer composition was determined by ¹H NMR spectroscopy. FTIR spectroscopy indicates the synthesis of random copolymers with different degrees of hydrogen bonding as measured by a shift of the OH vibration bands. The glass transition temperature of the random copolymers increases linearly with increasing DHPMA content, resulting in a positive deviation from the Fox equation. The thermal degradation of both homopolymers and their random copolymers has been studied. Finally, the solution behaviour of the copolymers and PDHPMA in water studied by dynamic light scattering showed a strong tendency of the polymer chains to form clusters in the size range of 15-62 nm. The size and the kind of associating interactions within the clusters strongly depend on the copolymer composition.     

Investigation of viscoelastic and thermal properties of cyclic carbonate bearing copolymers

In this paper, one-pot reaction of radical copolymerization of glycidyl methacrylate with methyl methacrylate, n-butyl acrylate and styrene under carbon dioxide atmosphere (1 atm) was employed to synthesize cyclic carbonate bearing copolymers. Obtained copolymers were characterized using ¹H NMR and FTIR spectroscopy. The viscoelastic and thermal properties of the resulted copolymers were investigated using dynamic mechanical thermal analysis and thermogravimetric analysis. Copolymer composition and monomer type had a significant effect on the properties of the copolymers. An increase in cyclic carbonate (2-oxo-1,3-dioxolane-4-yl-methyl methacrylate) content in the copolymer composition led to an increase in glass transition temperature, storage modulus and loss tangent as well as the thermal stability of the copolymers.     

Control of pH- and temperature-responsive behavior of mPEG-b-PDMAEMA copolymers through polymer composition

A series of poly(ethylene glycol) monomethyl ether-block-poly(2-(dimethylamino)ethyl methacrylate) (mPEG-b-PDMAEMA) diblock copolymers were synthesized using atom transfer radical polymerization to achieve controlled polymer molecular weight and narrow molecular weight distribution. The thermoresponsive properties of the mPEG-b-PDMAEMA diblock copolymers in aqueous buffered solutions were determined using UV-Visible spectroscopy and dynamic light scattering. The cloud point, a soluble-to-insoluble transition, was observed for all mPEG-b-PDMAEMA diblock copolymer solutions. Increasing either the mPEG or PDMAEMA molecular weight resulted in a decrease in observed cloud points as a function of pH and polymer concentration. Changing the mPEG molecular weight determined whether a second, higher temperature, thermal transition was observed as a function of pH and polymer concentration. Controlling the thermoresponsive properties of mPEG-b-PDMAEMA diblock copolymers through polymer composition, concentration, and pH enables the tailoring of these copolymers for applications ranging from non-viral gene delivery to use as a strengthening agent in paper.     

High‐Density Liquid‐Crystalline Polymer Brushes Formed by Surface Segregation and Self‐Assembly

High‐density polymer brushes on substrates exhibit unique properties and functions stemming from the extended conformations due to the surface constraint. To date, such chain organizations have been mostly attained by synthetic strategies of surface‐initiated living polymerization. We show herein a new method to prepare a high‐density polymer brush architecture using surface segregation and self‐assembly of diblock copolymers containing a side‐chain liquid‐crystalline polymer (SCLCP). The surface segregation is attained from a film of an amorphous base polymer (polystyrene, PS) containing a minor amount of a SCLCP‐PS diblock copolymer upon annealing above the glass‐transition temperature. The polystyrene portion of the diblock copolymer can work as a laterally mobile anchor for the favorable self‐assembly on the polystyrene base film.