## 1 Introduction  
Recently, as water shortage and pollution problems are becoming more serious, the importance of the water industry has become increasingly emphasized. Hence, membranes are receiving attention to play an important role in solving these water-related problems. Membranes have some advantages in comparison to traditional separation technologies such as coagulation, aggregation, and sedimentation which include convenience of control, excellent quality of processed water and ease of maintenance. Due to these advantages, membranes have been used for seawater desalination, sewage treatment, wastewater treatment, and drinking water production [1]. Membranes are divided into RO (reverse osmosis), NF (nanofliltration), UF (ultrafiltration), and MF (microfiltration) membranes, depending on usage. In particular, UF membranes make up a large part of the world membrane market and are used for wastewater treatment, and food concentration and purification. Polysulfone (PS), polyethylene (PE), polyethylene (PES), polyvinylidene fluoride (PVDF), and polyvinyl chloride (PVC) have been used in the production of membranes [2]. PVDF is an especially beneficial material to prepare membranes because of its strong chemical resistance and mechanical properties [3; 4; 5; 6; 7; 8]. Due to these advantages, PVDF has been widely used to fabricate membranes. However, PVDF has a critical disadvantage; it is susceptible to fouling during treatment of water containing humic acid which is a natural organic material (NOM). Since PVDF and NOM are hydrophobic, PVDF membranes easily absorb NOMs. As a result of filtration of NOM on PVDF membranes, its life is decreased. Hence, the improvement of PVDF membranes is recently a hot topic in membrane science. Among methods for improvement, blending with the graft copolymer in PVDF casting solution after synthesis of hydrophilic graft copolymer has been reported by researchers, in order to prepare PVDF membranes with improved flux during filtration of humic acid (HA) [9; 10]. However, it has not been fully clarified that successful PVDF-g-PHEA (Poly(vinylidene fluoride)-graft-poly(hydroxyethyl acrylate)) synthesis and blending with synthesized PVDF-g-PHEA additive in PVDF casting solution leads to improved hydrophilicity, resulting in improved ability during membrane formation. If the PVDF membrane has hydrophilic properties resulting from PVDF-g-PHEA, it will absorb less NOMs than the original PVDF membrane. Consequently, permeate flux can be enhanced by improving qualities of membrane material such as increased hydrophilicity [11]. Nowadays, ATRP (Atomic Transfer Radical Polymerization), one of the grafting methods, is used to develop membranes to include improvement of permeate flux. ATRP is utilized for polymerization of polymers containing halogen atoms and hydrophilic polymers containing styrene, (meth)acrylates, (meth)acrylates and acrylonitrile structures as the simple polymerization method which does not require strict experiment environment, comparing to other traditional polymerization methods [12; 13]. In advance, numerous graft copolymers such as poly(vinylidene fluoride)-graft-poly(ethylene glycol) methyl ether methacrylate (PVDF-g-PEGMA) and poly(vinylidene fluoride)-graft-poly(oxyethylene methacrylate) (PVDF-g-POEM) were successfully made by using ATRP method [14; 15]. Blending these graft copolymers with PVDF made membranes with improved permeate flux. HEA (Hydroxy acrylate) is the chemical material which contains acrylate structure. Therefore, it is expected that HEA would be polymerized with PVDF successfully by ATRP method to make the membrane, including hydrophilicity. Nevertheless, it has not been fully reported to synthesize PVDF-g-PHEA by ATRP method. For this reason, synthesis of PVDF-g-PHEA and fabrication of membranes containing PVDF-g-PHEA will be useful for the field of membrane technology in order to improve flux performances.