从溶胀平衡研究玻璃态高聚物的凝聚缠结网络

在13~15℃室温条件下对聚苯乙烯(PS)颗粒在二氧六环/水混合溶剂中的溶胀情况进行目视观察,可以看到,当减小混合溶剂二氧六环/水中的水含量时,PS颗粒从玻璃态到溶胀的玻璃态、溶胀的高弹态、流体态的转变,与PS颗粒升温时从玻璃态到高弹态、流体态的转变相对应.选定混合溶剂二氧六环/水(水6·8wt%)对一个单分散PS试样(Mw=1·68×105)在30℃进行分相平衡和溶胀平衡的测定.分相平衡是先将PS/二氧六环/水(混合溶剂水含量6·8wt%)体系加热到130℃使PS溶解成一均相溶液,然后在冷却过程中分相,在30℃达分相平衡(30天)时,浓相高分子体积浓度p″=0·304,稀相几乎为纯溶剂.从Flory-Huggins相平衡理论得出此体系的高分子-溶剂相互作用参数χ=0·63.本工作使用的单分散PS试样在选定的混合溶剂,即二氧六环/水(水6·8wt%)中,30℃时不能溶解只能溶胀,单分散PS颗粒淬冷试样(密度ρp=1·0451g/mL)到达溶胀平衡(80天)时浓相高分子体积浓度p″=0·308.而此淬冷试样经在80℃热处理100h后的老化试样(ρp=1·0470g/mL)达溶胀平衡(70天)时p″=0·312.从溶胀过程中浓相体积变化曲线可知试样经在80℃热处理过程中凝聚网络趋向于更均一,更接近热处理温度下的平衡态,试样密度增大,网络产生了新的链间凝聚,物理交联密度增大(凝聚点间分子量减小).从溶胀平衡理论并取χ=0·63(分相平衡)可得到淬冷试样的物理交联点间分子量Mc=11·6×104,老化试样的物理交联点间分子量Mc=6·9×104.实验结果说明溶胀过程及溶胀平衡的测定可以反映玻璃态高聚物中的凝聚网络结构的细节,而且非常敏感.

STUDIES ON THE COHESIONAL ENTENGLEMENT NETWORK OF POLYMERS IN GLASS STATE BY EQUILIBRIUM SWELLING

Equilibrium swelling in a non-solvent is a simple experimental method to reveal the cohesional entanglement network structure present in an amorphous polymer in its glassy state.In the present work results of visual observation of the swelling behavior of two PS granules in a series of dioxane/water mixed solvents are presented.On decreasing the water content in the mixed solvent a change of physical state of the PS granules from glassy state (water in dioxane ≥40 Vol%) to swollen glassy state (water in dioxane 35 Vol%～30 Vol%),to swollen rubbery state (water in dioxane 25 Vol%～20 Vol%) and to fluid state (water in dioxane 10 Vol%～5 Vol%) was observed.It corresponds to the change from glassy state to rubbery state and to fluid state on raising temperature of the granules.Base on these observations a mixed solvent of dioxane/water (water 6.8 wt%) was chosen for equilibrium swelling and phase separation equilibrium measurements for a monodisperse PS sample of M_w=1.68×10~5 at 30℃.In this mixed solvent PS granule can only swell but not dissolved.For the phase separation equilibrium the PS granule in the mixed solvent was first brought to 130℃ (in a sealed tube) to become a homogeneous single phase solution,then phase separation occurred on cooling and phase separation equilibrium at 30℃ was reached in 30 days to give a volume fraction of the polymer in the concentrated phase _p″=0.304.The dilute phase is practically the pure solvent.Monodisperse PS granules quenched from being heated to 120℃ for 30 min to erase thermal history of the sample (ρ_p=1.0451 g/mL) reached a swelling equilibrium in the mixed solvent in 80 days to give _p″=0.308.This quenched PS granules after being subjected to a sub-T_g annealing at 80℃ for 100 days (ρ_p=1.0470 g/mL) reached swelling equilibrium in the mixed solvent in 70 days to give _p″=0.312.From the curve of increasing volume of the swollen phase V_s(t),in mL/g PS,during the equilibrium swelling process it could be inferred that during sub-T_g annealing the cohesional network structure in the PS glass became more uniform,being closer to the equilibrium state at the annealing temperature,the van der Waals crosslinking density was increased,with tighter inter-chain cohesion resulting in higher density of the glass.If we take the polymer-solvent interaction parameter χ=0.63 obtained from phase separation equilibrium measurement,we obtained the molar mass between crosslinking points of the network,M_c=11.6×10~4 for the quenched sample,and M_c=6.9×10~4 for the annealed sample from Flory theory of network swelling.The experimental results clearly indicate that swelling process and swelling equilibrium measurements in a very poor solvent can offer a rather sensitive way to obtain some idea about the structure details of the cohesional network in polymer glassy state.