# Styrene-Based Copolymer for Polymer Membrane Modifications
## 1 Introduction  
Membrane modification of polymers by blending is a common and easy method that can provide many desirable properties such as solvent resistance, improved processability, hydrophilicity, and high productivity [1]. The poly(vinylidene fluoride) (PVDF) polymer is extensively employed for membrane preparation as it has an exceptional combination of mechanical, chemical, electrical, and thermal properties. However, the hydrophobic property of PVDF causes fouling and decreases the life of the membrane. Various methods for modification of PVDF have been reported [2; 3; 4; 5]. In one of these methods, the PVDF membrane surface was modified by grafting with active compounds using high-energy radiation [2]. Another method highlighted PVDF modification using a surface impregnation coating with active compounds such as hydroxypropyl cellulose (HPC) [3]. Radiation treatment was also suggested to create surface defects, which may act as active sites for the attachment of suitable compounds to the surface [4]. It has been well established that the mixing or blending of hydrophobic commercial polymers with active monomers such as acrylic acid increased hydrophilicity and enhanced their properties [5]. A styrene-based copolymer is a commercially available copolymer of styrene and acrylonitrile. Some key properties of styrene-acrylonitrile such as hydrogen bonding are similar to those of polysulfones [6]. A previous report has dealt with sulfonated styrene-acrylonitrile membranes, which were prepared and blended with cellulose acetate for performance enhancement [7]. The miscibility of polyethersulfone (PES) in hydrophilic copolymers containing 1-vinylpyrrolidone and styrene (PVP-S) has also been reported [8]. Ultrafiltration membranes were fabricated from the mixture of PES and (PVP-S) to improve the hydrophilicity of the hydrophobic PES membrane. [PERSON] and [PERSON] reported the influences of styrene on thermal degradation of polyacrylonitrile and influences of acrylonitrile on the depolymerization in polystyrene [9]. Cellulose acetate (CA)-styrene-acrylonitrileblend membranes were prepared with an additive like PEG, which achieved a higher flux than a 100% CA membrane [10].  
The prepared blend membranes have been effectively used for the aqueous separation of proteins such as BSA, EA, pepsin, and trypsin by ultrafiltration. Styrene-acrylonitrile/PVDF blends were prepared, where a phase separation was observed to occur with time. A transition from homogeneous nucleation and growth to nonlinear spinodal decomposition in the two-phase region was observed by atomic force microscope (AFM) phase imaging [11; 12]. In another example, a PVDF/styrene-acrylonitrile blend was prepared by solution blending, where the acrylonitrile segment of the styrene-acrylonitrile copolymer was found to be partially miscible with PVDF [13]. However, the styrene segment reduced the copolymer's polarity and consequently its miscibility with PVDF. Similar results have been reported for styrene-acrylonitrile/PVDF by melt blending [14]. In our earlier study, we reported PVDF/styrene-acrylonitrile blend membranes that exhibited partial miscibility with less than 50 wt. % styrene-acrylonitrile in PVDF for textile wastewater treatment [15]. The prime objective of the present work is to report the crystallinity, phase analysis, thermal stability, and surface morphology of these polymer blends.