用热焓松弛行为研究聚苯醚和改性聚苯醚共混体系的相容性

用DSC分别探讨了苯酰化聚苯醚(PPO)(BA~(31.0)-PPO和BA~(43.4)-PPO)/PPO共混体系的热焓松弛变化规律与差异.发现已知是相容体系的BA~(31.0)-PPO/PPO在低于T_g等温退火过程中只出现一个吸热峰;典型的相容体系PPO/PS也表现出类似的行为.而未知相容性的BA~(43.4)-PPO/PPO在等温退火过程中出现两个吸热峰,此两峰的T_p值随退火时间的变化类似于各纯组分相应条件下的变化.电子显微镜结果表明,BA~(43.4)-PPO/PPO是相分离体系.因此对T_g非常接近的较刚性主链的PP0及其改性物的共混体系可用热焓松弛行为确定其相容性.     

聚苯醚羧酸酯对C-PPO/PS共混体系的增容作用

前曾报道羧化度为8～lOmol%的羧化聚苯醚(C-PPO)与PS共混体系具有UCST和LCST共存的特殊相行为^[1],而羧化度大于11.6mol%时,C-PPO/PS共混体系表现出不相容性^[2,3]。化学改性PPO可作为PPO与其他聚合物共混的增容剂。本文讨论C-PPO的正十二酯(Lau-CPPO)对C-PPO/PO共混体系混溶性的影响。     

过剩热焓松弛CO_2和甲苯在PET薄膜中渗透的影响

本文研究了非晶态、未取向PET薄膜样品在低于T_g温度以下热处理,结构的变化和过剩热焓松弛对CO_2和甲苯溶剂在样品中渗透速率的影响。结果表明,随退火时间增加,从T_g转变吸热峰确定的过剩热焓松弛量、 T_g温度、密度增加,而反式构象含量减少。除分子链堆砌密度提高或自由体积下降外,没有发现非晶相有结构上的变化。因此,CO_2在样品中随退火时间的增加渗透速率下降。然而,由于样品脆性增加和甲苯的溶胀作用,样品表面出现裂纹,使甲苯在样品中的表观渗透速率增加。     

改性PPO的溶解性能研究

研究了 PPO、羧化 PPO(C-PPO)、苯酰化 PPO(BA-PPO)、苯磺酰化 PPO(BS-PPO)和磺化 PPO(S-PPO)在不同溶剂中的溶解能力,分别讨论了各种取代基以及取代度对溶解性能的影响,测定了各种改性 PPO 在溶剂中的特性粘数,估计了它们的溶度参数。发现,在 PPO 的溶解过程中,色散力起重要作用,S-PPO 样品的溶解过程则是极性力和氢键起主导作用,而 BA-PPO 和 BS-PPO 的溶解过程则是三种力相互作用的结果。对于不同取代度的 C-PPO,随取代度增加,在极性和形成氢键的溶剂中的溶解能力增加。     

聚苯醚羧酸盐的聚集态结构

本文用热学、力学和散射方法研完了聚苯醚羧酸盐的链结构、羧化聚苯醚(C-PPO)在二氧六环溶液中用0.5 NaOH或CsOH的醇水溶液中和成钠型或铯型的C-PPO离聚体,用DSC测定一系列羧酸盐含量的C-PPO离聚体的玻璃化转变温度得到形成离子微区的临界阳离子浓度约为5mol％;动态力学谱中在高于玻璃化转变温度域出现的α松弛峰亦证明了微相结构的存在;SAXS结果表明其离子微区的尺寸约为30(?),其尺寸大小和离聚体中阳离子浓度无     

木糖醇玻璃焓松弛的量热分析

为了考察木糖醇的玻璃化转变和焓松弛行为,寻求碳链长度对线性多元醇玻璃化转变和焓松弛行为的影响,利用差示扫描量热(DSC)技术测定了不同降温速率下木糖醇在玻璃化转变温度(Tg)前后的比热容(Cp),通过曲线拟合获得了TNM(Tool-Narayanaswamy-Moynihan)模型参数,并和其他多元醇类已有研究结果进行对照.结果表明,尽管TNM模型可以很好地重现不同降温速率体系的实验比热容数据,但模型参数并不是材料常数,而是和热历史有关,不同的降温速率对应不同的模型参数.指前因子(A)、非线性参数(x)和非指数参数(β)均随着降温速率的增加而降低,松弛活化焓(△h*)的变化趋势刚好相反.几种线性多元醇玻璃化转变和TNM模型参数的对照表明,玻璃化转变温度,松弛活化焓和动力学脆度(m)都随着烷基碳链长度的增加而增加.虽然非线性参数、非指数参数随碳链长度的增加有降低的趋势,但木糖醇展现出反常变化的情形.     

改性PPO的溶解性能和溶度参数的初步估计

研究了聚苯醚PPO、羧化PPO、苯酰化PPO、苯磺酰化PPO和磺化PPO在不同溶剂中的溶解能力,分别讨论了各种取代基以及取代度对聚合物溶解性能的影响,由PPO衍生物的特性粘数估算了它们的溶度参数。     

退火条件对山梨醇玻璃焓松弛参数的影响

采用差示扫描量热法(DSC)测定山梨醇样品经历不同时间(t_a)等温退火后, 以10 K·min^-1速率进行升温时玻璃化转变温度(T_g)前后的比热容(C_p(T)). 将Gómez Ribelles (GR)提出的一种基于构型熵的现象学模型用于描述山梨醇玻璃的焓松弛行为, 考察GR模型能否适用于小分子玻璃体系. 结果表明, 单组GR模型参数拟合的曲线均能较好重现对应热历史条件下的山梨醇体系的实验所得C_p(T)曲线, 尽管并未找到不随热历史而变的一组参数作为材料常数, 但与其它现象学模型应用于小分子玻璃时, 其模型参数都随热历史变化而变化的特点相比, GR模型的某些参数基本保持不变. 且在较长退火时间下拟合得到的模型参数普适性较好. 同经历连续降温的山梨醇相比, 等温退火过程得到的松弛极限态参数(δ)的平均值与T_g处比热容增量(ΔC_p(T_g))的比值明显增大, 但仍小于聚合物的值, 表明GR模型提出的亚稳极限态对小分子玻璃的影响值得商榷.     

热处理对尼龙1010固态结晶和玻璃态热松驰的影响

本文用DSC首先论证淬火尼龙1010试样在DSC曲线上出现的放热峰是冷结晶峰,然后研究淬火尼龙1010在不同热处理条件下,冷结晶峰和玻璃态热松驰峰的变化规律。实验结果表明,等温结晶时间较短,试样的固态结晶速率较快;等温结晶时间较长,固态结晶速率较慢,这可能与在Tg区域等温所形成的新氢键有关。当升高等温温度时,固态结晶速率加快。在低于Tg的不同温度退火,玻璃态热松弛峰的峰高及热焓在281K达最大值,进而确定对玻璃态热松驰影响最敏感的温度区间是277～284K。     

基于位形熵模型的山梨醇玻璃焓松弛的量热分析

利用DSC技术考察了无定形山梨醇体系的焓松弛行为, 在10 K•min^－1的升温速率下测定了经历不同降温速率(0.5～20 K•min^－1)的山梨醇在玻璃化转变(T_g)前后的比热容[c_p(T)]. 利用基于位形熵演变的焓松弛现象学模型(GR模型)模拟了实验数据. 不论是否假设松弛过程存在一个亚稳极限态, 模型参数均能很好地重现经历不同热历史体系的升温c_p(T)曲线. 在物理意义明确的模型参数组中, 除了非指数参数随降温速率的增加而增加外, 其余均不随热历史的变化而变化. 拟合较低降温速率下c_p(T)曲线获得的GR模型参数的预测力明显好于在较大降温速率下获得的结果. 由于松弛时间对拟合过程中选择的“固定参数”的取值很敏感, 因此模型能否预测体系的比热容不能看成确定松弛时间的唯一依据. 在利用GR模型分析无定形山梨醇体系的脆度时, 如果选择极限假想温度作为T_g, 会导致计算结果明显小于文献值.     

Influence of the chemical structure on the kinetics of the structural relaxation process of acrylate and methacrylate polymer networks

The enthalpy relaxation of poly(hydroxyethyl methacrylate) (PHEMA), poly(ethyl methacrylate) (PEMA) and poly(ethyl acrylate) (PEA) networks, obtained by DSC, are compared. The temperature interval of the glass transition broadens in the sequence PEA-PEMA-PHEMA. The plots of the enthalpy loss during the annealing for 200 min at different temperatures below T_g show that the structural relaxation process also takes place in PHEMA in a broader temperature interval than in PEA or PEMA. The modelling of the structural relaxation process using a phenomenological model allows determining the temperature dependence of the relaxation times concluding that the fragility in PHEMA is significantly lower than in PEMA. Both features are ascribed to the connectivity of the polymer chains in PHEMA via hydrogen bonding. The role of the presence of the methyl group bonded to the main chain is analysed by comparing the results obtained in PEA and PEMA.     

Orientation and relaxation study of polystyrene: Polystyrene/poly(phenylene oxide) blends

Polarization modulation infrared linear dichroism has been used to study the molecular orientation and relaxation of polystyrene/poly(2,6‐dimethyl 1,4‐phenylene oxide) (PS/PPO) miscible blends, containing up to 20% PPO, during and after a rapid uniaxial deformation above T_g. In general, it is found that both the PS and PPO chain orientation functions increase with stretching rate and PPO content, and decrease with temperature. For all blends investigated, between T_g + 5 and T_g + 13 °C, the relaxation occurs at the same rate for PS and PPO and, therefore, the relaxation times calculated are similar indicating, under those conditions, a strong relaxation coupling between the two polymers at both short and long times. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1405–1415, 2000     

Glass transition and enthalpy relaxation of ethylene glycol and its aqueous solution

Differential scanning calorimetry (DSC) and cryomicroscopy were employed to investigate the glass transition and enthalpy relaxation behaviors of ethylene glycol (EG) and its aqueous solution (50% EG) with different crystallization percent. Isothermal crystallization method was used in devitrification region to get different crystallinity after samples quenched below glass transition temperature. The DSC thermograms upon warming showed that the pure EG has a single glass transition, while the 50% EG solution has two if the solution crystallized partially. It is believed that the lower temperature transition represents the glass transition of bulk amorphous phase of EG aqueous solution glass state, while the higher one is related to ice inclusions, whose mobility is restricted by ice crystal. Cryomicroscopic observation indicated that the EG crystal has regular shape while the ice crystal in 50% EG aqueous solution glass matrix has no regular surface. Isothermal annealing experiments at temperatures lower than T_g were also conducted on these amorphous samples in DSC, and the results showed that both the two amorphous phases presented in 50% EG experience enthalpy relaxation. The relaxation process of restricted amorphous phase is more sensitive to annealing temperature.     

Glass‐formation kinetics of miscible blends of atactic polystyrene and poly(2,6‐dimethyl‐1,4‐phenylene oxide)

We present a detailed investigation of the kinetics associated with the glass transitions of miscible blends composed of atactic polystyrene (a‐PS) and poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO). According to both dynamic mechanical analysis and differential scanning calorimetry, relaxation times displayed an enhanced temperature dependence (i.e., more fragile or more cooperative behavior) for the blends compared with additive behavior based on the responses of neat a‐PS and PPO. This is consistent with the notion that specific interactions between the blend components heighten the intermolecular cooperativity. The compositional dependence of fragility provided insight into physical aging results for the properties of volume and enthalpy. The combination of our research and a previously reported pressure–volume–temperature study by Zoller and Hoehn (J Polym Sci Polym Phys Ed 1982, 20, 1385) provided evidence that the observation of increased glassy densities for the blends compared with those of the pure polymers was kinetic in origin and was not a feature of the thermodynamics of miscibility. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2118–2129, 2001     

三甲基硅取代PPO和三苯基硅取代PPO及其气体选择透过性能

讨论了聚２，６－二甲基－１，４－苯撑氧（ＰＰＯ）与三甲基氯硅烷和三苯基氯硅烷的反应，合成了一系列取代含量不同的三甲基硅取代ＰＰＯ（ＴＭＳ－ＰＰＯ）和三苯基硅取代ＰＰＯ（ＴＰＳ－ＰＰＯ）．研究了取代基团不同和取代含量变化对聚合物的气体选择透过性能的影响，发现ＴＭＳ－ＰＰＯ的气体透过系数随三甲基硅取代量加大而增高，分离系数下降；ＴＰＳ－ＰＰＯ的气体透过系数和分离系数都随三苯基硅取代量的增加而下降，ＴＰＳ－ＰＰＯ与ＴＭＳ－ＰＰＯ的气体溶解系数相近，扩散系数差别较大．故二者气体透过系数的不同主要是由于扩散系数的差异．从化学结构与气体透过性能关系的角度来看，若在聚合物分子中引入有较小转动自由能的大基团，则有利于气体分子的扩散透过．     

Enthalpy relaxation of rigid poly(vinyl chloride)

The changes which take place on annealing rigid PVC in the vicinity of the glass transition have been followed by differential scanning calorimetry. The changes appear as an increase in the glass-transition temperature and a decrease in the enthalpy with time of annealing. For annealing at 75°C, the enthalpy after 50–100 hr approaches the value characteristic of the equilibrium liquid state. The results obtained for annealing at 65°C and 75°C are in accord with those expected for the relaxation of an amorphous material, and are at variance with those expected on the basis of crystallization taking place on annealing. The enthalpy relaxation process is characterized by a distribution of activation energies centered about 18.8 kcal mole^?1, and seems to reflect a multiplicity of molecular processes.     

Local compositional fluctuations in PPO/HIPSand PPO/SBS blends

Solid-state NMR relaxation has been used to explore the distribution of components in poly(phenylene oxide) (PPO) high impact polystyrene (HIPS) and PPO/poly(styrene-b-butadiene-b-styrene) (SBS) blends. The nuclear relaxation of PPO in the former system is single exponential for all compositions, but the relaxation of PS in the blend is simple exponential only when the PPO content is low but is otherwise nonexponential. The nuclear magnetization decay curves were analyzed in terms of statistical compositional fluctuation at the scale of spin diffusion distances of several nm. Distribution functions for nuclear relaxation and for blend composition have been derived. Extraction of low molecular weight occluded PS from HIPS resulted in blends having reduced homogeneity. Addition of low molecular weight PS enhanced homogeneity in both the PPO/HIPS and PPO/SBS blends. © 1994 John Wiley & Sons, Inc.     

不同结晶度的乙二醇及其水溶液玻璃化转变与焓松弛

为了考察晶体成分对无定形成分玻璃化转变和结构松弛行为的影响,利用差示扫描量热法(DSC),结合低温显微技术,研究了乙二醇(EG)及其50％水溶液在不同结晶度时的玻璃化转变和焓松弛行为.采用等温结晶方法控制骤冷的部分结晶玻璃体中的晶体份额.DSC结果表明,对于部分结晶的EG,只有单一的玻璃化转变过程,而对于50％EG,当结晶度不同时,不同程度地表现出两次玻璃化转变（无定形相Ⅰ和无定形相Ⅱ）.相Ⅰ的玻璃化转变温度和完全无定形态的含水EG的玻璃化转变温度相一致;相Ⅱ的玻璃化转变温度要比此温度约高6 ℃.低温显微观察结果印证了DSC实验结果.DSC等温退火的实验和KWW(Kohlrausch-Williams-Watts)衰变函数分析结果表明,EG无定形和50％EG中的两种无定形有不同的焓松弛行为.     

Glass Transition Behavior in Se-Rich Ge-Se Alloys

Differential scanning calorimetry (DSC) was utilized to study the behavior of six Ge-Se glasses containing 0, 5, 10, 15, 17.5 and 20 at.% Ge during the glass transition. These alloys readily form glasses and can be prepared by quenching in air. Moreover, their behavior depends greatly on the composition. This work reveals that two additional properties must be considered: the variation in the glass transition temperature and different structural relaxation. The quantity used to quantify the relaxation was the enthalpy relaxation as this measures the heat lost by the glass during annealing. Given the complexity of the relaxation process, the experimental results were analysed by means of the empirical Kohlrausch-Williams-Watts relaxation model. This revised version was published online in July 2006 with corrections to the Cover Date.